破坏性旋涡诱导下大跨屋盖表面风荷载机理研究

For large-span roofs, separation bubble and conical vortices are well known as their destructiveness. Roofs under those vortices are exposed to extremely high suctions, especially at roof corners and leading edges, which finally causes catastrophic destruction. Therefore, the mechanism of wind loads under organized vortices on flat roofs, arch roofs and gable roofs are investigated in this project, with the aim of predicting and controlling greater suctions generated by these destructiveness vortices. Firstly, through pressure measurements in wind tunnel and CFD, the characteristics and mechanism of wind loads on flat roofs, arch roofs and gable roofs are studied. The influence of roof geometrical feature on vortices and suctions were then explored. Secondly, based on measured velocities by PIV experiment, a two-dimensional vortex model is established. The quasi-steady theory is corrected by including the effect of the vortex model. With the flow model and the corrected quasi-steady theory, suctions on separated regions of the flat roofs, arch roofs and gable roofs are then predicted, which are verified by the measured data. Thirdly, aerodynamic measures, which can be employed to suppress vortices and the induced suctions, are researched. The effectiveness of each aerodynamic measure for various roofs is discussed by pressure measurements and the PIV technique. The parameters of the aerodynamic measures are then optimized to improve the efficiency. Results of this research project could provide substantial theoretical foundation for the wind-resistant design of large-span roofs.

大跨屋盖表面最具破坏性的旋涡是分离泡和锥形涡。在此作用下，屋盖局部将出现强风吸力，引起分离区破坏，最终造成屋盖整体失效。因此，本课题以分离泡和锥形涡为切入点，对不同屋盖（平屋盖、双坡屋盖和拱形屋盖）表面风荷载机理进行研究，以期合理预测及控制旋涡诱导的风吸力。首先，基于风洞测压试验和CFD计算，研究不同风向下平屋盖、双坡屋盖和拱形屋盖表面风荷载特性及其产生机理；考察屋盖几何特征对于旋涡形态及风吸力的影响。其次，基于流动显示试验（PIV）测得的旋涡流速，建立二维简化流动模型，据此对传统准定常理论进行修正，给出分离区内风吸力的预测方法，并予以验证。最后，通过风洞测压试验和流动显示试验（PIV），探讨各种气动措施（迎风角倒角化、迎风前缘曲线化和护墙）对于抑制旋涡作用、减小涡致吸力的有效性；并对各气动措施进行参数优化，提高其使用效率。所得结论将为大跨屋盖抗风设计提供合理的理论依据，使风灾可防、可控。

大跨屋盖表面最具破坏性的旋涡是分离泡和锥形涡。在此作用下，屋盖局部将出现强风吸力，引起分离区破坏，最终造成屋盖整体失效。因此，本课题以分离泡和锥形涡为切入点，对平屋盖和双坡屋盖表面风荷载机理进行研究，以期合理预测及控制旋涡诱导的风吸力。首先，通过刚性模型风洞测压试验，研究了分离泡和锥形涡作用下，平屋盖和双坡屋盖表面风压的分布特性、脉动特性和相关特性；特别地，对于双坡屋盖，根据所得风压分布特性和风压统计极值，建议将双坡屋盖分为低坡度、中等坡度和高坡度三类；低坡度的屋盖表面可分为角部、长边边缘、短边边缘和中部4个区域，中等坡度和高坡度的屋盖表面可在此基础上进一步细分出屋脊区域以及短边边缘与屋脊的交接区域。其次，通过流场显示试验（PIV），测得锥形涡内部流速，结合现有兰金涡模型和Banks模型，建立了简化的二维锥形涡流动模型。据此模型给出了旋涡流速、旋涡内部流线曲率和屋面吸力三者间的关系，发现当旋涡内部流线曲率和旋涡流速增大，旋涡强度提高，屋面风吸力增大。此外，采用该流动模型，可实现对平屋盖表面锥形涡和分离泡涡核下吸力的有效预测，预测误差小于15%。最后，通过刚性模型风洞测压试验，研究了倒角化迎风前缘和扰流板对于平屋盖表面风压分布、风压脉动以及面积平均风压的影响。结果表明，倒角化迎风前缘可减小旋涡作用区内的风吸力，但迎风前缘附近风吸力可能增大。45°风向角下，当迎风前缘倒角半径达25mm和35mm时，平屋盖角部面积平均风压极值的降幅分别为48%和59%。沿屋盖周边布置的扰流板亦可减小分离泡作用区内的风吸力，降低该区域风压的非高斯脉动特性。0°风向角下，当扰流板倾角为0°、10°和20°时，平屋盖表面倾覆力矩的降幅分别为18.2%、21.9%和23.3%。